Wireless networks may be used to transmit signals from devices that are only activated rarely. For example, a sensor detecting glass-breakage in a security alarm system may only rarely be activated. In such a design, the system may continuously power the sensor and processor to monitor for glass breakage while the associated wireless transceiver may be powered-down to save battery power. Upon detecting glass breakage, the sensor/processor module can power up the associated wireless transceiver and use it to transmit signals associated with the detected event to a central control panel. This works to “wake up” the transceiver from within the device. But how could the control panel query the status of the glass breakage detector since its transmitter is normally in the off state—that is, “wake up” the transceiver from outside the device?
Such a dilemma increases in importance in the case of implanted devices. Consider for example an implanted medical device such as a combination heart monitor/defibrillator that is implanted in a person's body. In like manner to the previous example, the heart monitor could “wake up” a powered-down associated transceiver upon detecting a dangerous heart condition or a heart attack. But how could a medical professional access the heart monitor when the transceiver is in the powered-down state?
In the art are known systems to manage the power condition of the transceiver and yet make it available to receive external requests. For example, the transceiver may power up on a schedule and check for messages. The schedule may be synchronized with the associated network or it may be intrinsic only to the transceiver itself. This scheduling approach allows the transceiver to be shut down most of the time and so conserve precious battery power. There are at least two problems with this method. First, the transceiver is still being powered-up; using what is often critical battery power. Indeed, in some transceiver systems, the receiving component draws more power than the transmitting component. Second, some wireless networks require acquisition time for the network to synchronize, handshake, verify security protocols, etc. This can be a time consuming and by correlation, a power consuming process. For many devices that may be associated with wireless networks, this is an unacceptable solution because the power draw cannot be supported.
U.S. Pat. Nos. 5,115,236, 5,553,058, and 5,973,611 show the use of signals to remotely wake up a receiver. U.S. Pat. Nos. 3,145,380 and 4,963,887 show the use of transmitted radio frequency energy to provide energy to a responder system.
What is needed in the art is a system to activate a transceiver, such system requiring little or no power draw of its own. In addition, it is preferable that the activation signal be transmitted on a network (i.e., frequency or data communications protocol) distinct from the primary network used by the receiver to be activated.